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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="xmlsec-notes-verify"></a>Verifying a signed document</h2></div></div></div>
<p>The typical signature verification process includes following steps:
	  </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem"><p>
		Load keys, X509 certificates, etc. in the <a class="link" href="xmlsec-keysmngr.html#xmlSecKeysMngr" title="struct xmlSecKeysMngr">keys manager</a> .
	    </p></li>
<li class="listitem"><p>
		Create signature context <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a>
		using <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxCreate" title="xmlSecDSigCtxCreate ()">xmlSecDSigCtxCreate</a> or
		<a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxInitialize" title="xmlSecDSigCtxInitialize ()">xmlSecDSigCtxInitialize</a>
		functions.
	    </p></li>
<li class="listitem"><p>
		Select start verification 
    		<a class="ulink" href="" target="_top">&lt;dsig:Signature/&gt;</a>
		node in the signed XML document.
	    </p></li>
<li class="listitem"><p>
		Verify signature by calling <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxVerify" title="xmlSecDSigCtxVerify ()">xmlSecDSigCtxVerify</a> 
		function.
	    </p></li>
<li class="listitem"><p>
		Check returned value and verification status (<em class="structfield"><code>status</code></em>
		member of <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a> structure).
		If necessary, consume returned data from the <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">context</a>.
	    </p></li>
<li class="listitem"><p>
		Destroy signature context <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtx" title="struct xmlSecDSigCtx">xmlSecDSigCtx</a>
		using <a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxDestroy" title="xmlSecDSigCtxDestroy ()">xmlSecDSigCtxDestroy</a> or
		<a class="link" href="xmlsec-xmldsig.html#xmlSecDSigCtxFinalize" title="xmlSecDSigCtxFinalize ()">xmlSecDSigCtxFinalize</a>
		functions.
	    </p></li>
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<p>
	</p>
<p>
	     </p>
<div class="example">
<a name="id-1.2.8.3.3.1"></a><p class="title"><b>Example 14. Verifying a document.</b></p>
<div class="example-contents">
<pre class="programlisting">
/** 
 * verify_file:
 * @xml_file:		the signed XML file name.
 * @key_file:		the PEM public key file name.
 *
 * Verifies XML signature in #xml_file using public key from #key_file.
 *
 * Returns 0 on success or a negative value if an error occurs.
 */
int 
verify_file(const char* xml_file, const char* key_file) {
    xmlDocPtr doc = NULL;
    xmlNodePtr node = NULL;
    xmlSecDSigCtxPtr dsigCtx = NULL;
    int res = -1;
    
    assert(xml_file);
    assert(key_file);

    /* load file */
    doc = xmlParseFile(xml_file);
    if ((doc == NULL) || (xmlDocGetRootElement(doc) == NULL)){
	fprintf(stderr, "Error: unable to parse file \"%s\"\n", xml_file);
	goto done;	
    }
    
    /* find start node */
    node = xmlSecFindNode(xmlDocGetRootElement(doc), xmlSecNodeSignature, xmlSecDSigNs);
    if(node == NULL) {
	fprintf(stderr, "Error: start node not found in \"%s\"\n", xml_file);
	goto done;	
    }

    /* create signature context, we don't need keys manager in this example */
    dsigCtx = xmlSecDSigCtxCreate(NULL);
    if(dsigCtx == NULL) {
        fprintf(stderr,"Error: failed to create signature context\n");
	goto done;
    }

    /* load public key */
    dsigCtx-&gt;signKey = xmlSecCryptoAppKeyLoad(key_file,xmlSecKeyDataFormatPem, NULL, NULL, NULL);
    if(dsigCtx-&gt;signKey == NULL) {
        fprintf(stderr,"Error: failed to load public pem key from \"%s\"\n", key_file);
	goto done;
    }

    /* set key name to the file name, this is just an example! */
    if(xmlSecKeySetName(dsigCtx-&gt;signKey, key_file) &lt; 0) {
    	fprintf(stderr,"Error: failed to set key name for key from \"%s\"\n", key_file);
	goto done;
    }

    /* Verify signature */
    if(xmlSecDSigCtxVerify(dsigCtx, node) &lt; 0) {
        fprintf(stderr,"Error: signature verify\n");
	goto done;
    }
        
    /* print verification result to stdout */
    if(dsigCtx-&gt;status == xmlSecDSigStatusSucceeded) {
	fprintf(stdout, "Signature is OK\n");
    } else {
	fprintf(stdout, "Signature is INVALID\n");
    }    

    /* success */
    res = 0;

done:    
    /* cleanup */
    if(dsigCtx != NULL) {
	xmlSecDSigCtxDestroy(dsigCtx);
    }
    
    if(doc != NULL) {
	xmlFreeDoc(doc); 
    }
    return(res);
}
		</pre>
<p><a class="link" href="xmlsec-verify-with-key.html#xmlsec-example-verify1" title="verify1.c">Full Program Listing</a></p>
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